Synephrine is a sympathomimetic phenylethylamine derivative that occurs naturally in citrus fruits. It is often added to dietary supplements intended for weight loss and enhancement of sports performance, typically in the form of Citrus aurantium extracts and in many cases in combination with caffeine. The health risks of synephrine were evaluated on the basis of the available toxicological data and in accordance to the EFSA guidance on the safety assessment of botanicals and botanical preparations intended for use in food supplements. In animal studies, orally applied synephrine induced adrenergic effects on the cardiovascular system (increase of blood pressure, ventricular arrhythmias), which were enhanced by the concomitant application of caffeine as well as physical activity. Some human intervention studies investigating the acute effects of synephrine on blood pressure and heart rate of healthy, normotensive test persons indicate that synephrine can induce cardiovascular effects in humans. A series of published case reports of adverse cardiovascular effects (hypertension, cardiac arrhythmia, myocardial infarction) were associated with consumption of synephrine- and caffeine-containing dietary supplements. In conclusion, consumption of high amounts of synephrine, especially in combination with caffeine and physical exercise, is associated with an increased risk of adverse effects on the cardiovascular system. According to the assessment by the BfR (Bundesinstitut für Risikobewertung), daily intake of synephrine through dietary supplements should not exceed the median intake from conventional foods.
Keywords: Bitter orange extracts; Botanicals; Caffeine; Citrus aurantium; Food supplements; Synephrine.